What quantity is measured by a battery rating givenj/,oke-ue+n * te)ykm in ampere-hours $(A\cdot H)$ ?

When an electric cell t 9u di l.,t6:sfxtnqt35 .b(ts.tjnois connected to a circuit, electrons flow away from the negative terminal in the circuit. Butt5l. i st.(o q 6,:ubnjttdfsn9t3.xt within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, batt5z13ut.ctf w8e 1xkufx+v /fkery voltage, battery enevt1xuztfx.1kff/u3 kw 5 ec 8+rgy, battery power, or battery resistance? Explain.

One terminal of a car batte) i n8s:xmis+ufgogl0ansf3sch )3 +/ry is said to be connected to “ground.” Since it is not really connected to t g+fn0u: 3xsissglh3c a/ns+8f)om)i he ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. You do hqj3u6m/fu,c n’t have to wait for water to flow from the faucet valve h3 6mqu/,c fujto the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the sa*kk*x2+;dkrw g i0whsme length have the same resistancrkk0 g2;ww*+ sihk dx*e? Explain.

If the resistance of a small immersion heater (to heat wat68*y wmj rf(5uzn7onper for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heatinj 6wp8umz*nf (ryo5n7g process? Explain.

If a rectangular solid made of carbon has sides of lengths a, m ;.6hrnnn4x yul 0zgd3fm)+l 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) t nn ylm+uxhmf60dgnl; z r3).4he least resistance, (b) the greatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a lightbulb q0v m 4*1qkjo/g5 diqsp3n( ftburns out?

Explain why lightbulbs almost always burn out just as they are turned onrv u/z9.3hdf d and not after they hav 9rhz.v3u /ddfe been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has b9sk0gr7 f5qz9u )mwl f.m4zgthe higher re7kur bfgm 0g9.5fzlqsz w)m49sistance?

Electric power is transferred +aw wpedt:)i0h4jy 5mover large distances at very high voltages. Explain how the high volmdw0y4:pe)h iw+ ta5j tage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to r baepp3iy7 5eh* um5f7eplace this fuse with a 25-A fusep57 aupm i3*5fb yh7ee?

When electric lights are operated on low-frequency ac (say, 5 Hz), they f: .a 2chnhnxt-licker hc:t-nn.x a2hnoticeably. Why?

Driven by ac power, the same elecd 5uywywr,ay4hpc3 + .yb5k5 c tfxh;.trons pass back and forth through your reading lamp over and over again. Explain why the lighwy;h, +y yy.xcpd5trk3a4cw5.bf 5u h t stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediatn8ifftf)w/jp 8q4i .lely after the i488wf)tjln/q i.fpftoaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? 0x3a+y q-x) dw8 )i s(x y6jqrlvorps;Explain.

Different lamps might have batteries coed.- (zggszlmgqm l1*;9j yy :nnected in either of the two arrangements*j;e1:9.z(qmy sgzll g - dmyg shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons arcgu2t5jp,y31m 8hl ve e flowing past any point in t5 vmlep1 ,tjch32u gy8he wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery usink 1e6gjwc*x k)g a current of 6.7 A for 5.0 h. How much charge passes through the batterjcw) g6e*1kxk y?    $ \times10^{ 5}\;C$

  What is the current in ampegbnycuds2qiq lbum8 ( b(qyh0 vln+,/, ,e 2s1res if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces p ,htjo89t4xh a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A oqmw *ez9e,:wa5 c yos0f current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A wh dclug.riiyco)vzj 3r87/ 1*my (fn-xen plugged into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with a resiy uv2yd;7f z,c76d;b ty(m mwcstance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb 66r mnqm: .m:wo:drsbwhose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electri 73ea1:ab, .shzan gbuor;w u;w 8zc1ec transmission line carrying 2800 A (Fig. 18–34). The lineo1bc.wwe;z gu7 :;rs3 a,1a8bnauhz e has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A at 240 V. j u+,)b , rdt)qi/m 7qutn(8jccuqsk6
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.j;.f0x(gd a 5yf6los l60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m lengthfb)yq+g j o2svl, 98js of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of cou w5x 95agevw ;3k5cxhpper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resist eenjm-kieze -+ 4es81ance of 10.0 m of aluminum wire 2.0 mm in diameter, to ke1e m-je+eezsn 8 4i-20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the s i et+/;n7d/ony;qgo+m2v 4fgylw1tvame resistance as a tungsten wire of the same length? G/;/m t + vg+7ndiw; qg1yvofto4eyln2 ive numerical details.    mm

  A certain copper wire has au ijth;tz/x70 resistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the tk(.ek8o ult76 s-xhetemperature of a copper wire (originally ato7ttk.ehxs 6( -el8ku $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have thn v e,ns-c*s h2,-/l4mmvl ctje same resistivity as tungsten does ansv ,ntl4cevjm*hl, 2c/s-- mt $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistan5q qq, l7crot,ce of about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26-m lengthdu5 ylst*0d,w ow2 w0v of household no. 14 copper wire (used in 15-A cirltudov wws0y,5d0 2*wcuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbymymzv w,t xu 1i06a16on has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively uymi,a101 vxztwmy66 (Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the sam; g)s znp-vn-pe resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter;v pn-pz g)-ns wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is conopal*o j bd1,k7 :rc7lnected to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measured at oa7 ,7jolkb:c pr *l1d20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m o ,fie( 2n6(qlze8yerff copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wire.f8l( (z r2e6qenef,i y
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it.wa0) mjbz o ;4p9orgk2)zix d is important that the value of a resistance not change with temperature. For example, suppose you made ak rwp )o;mj4ziogz x)9b. ad02 $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element yk8 e9s31kq mfof an electric oven is designed to produce 3.3 kW of heat when connected to a 240-V source. W9ye13m qsk 8fkhat must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-gsr luze:r0s (l *bih+3chg+v- ybr 81V portable CD player that draws a maximum of 320 mA of 1 0sserl+g b:rv*u (+hyzl r3-bghi8 ccurrent?    W

  What is the maximum voltage that can be applied acrow fr3n*y2v2x pss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current throf)q oyi6uarx+8,d5 w8 pgvv3g ugh, a 75-W lightbulb connected to its proper source voltage opg88fiq vd53)vg,a u yow+6xrf 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 110 W. vm,+dd,gbi 7ehwf1jbw2j2q:j.j ix; Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settingslxg7k)8nq qv+ (vr,oh: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity if4y.v2*x- :n ncbkao xj,foe12r+d avs delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V v24fe fxo 2j,yn:nxcd ab.kr +1 *avo-bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does p p vdlxzybx 9,q6-20ka 550-W toaster use in the morning if it is in operation for a total of 15 min? At a cost of bd,z-xx vpplyk6 09 2q$9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it cost to leave a 25-W por-3(( db kusiharhn, l;ch light on day and night f,ik3-lsb d (nhharu(; or a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 9wd zjqq1y)j)) z9: o vwuziq gsr6h3)1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when)3zgh s9wrqj :djzq)uqv19)wz 6i o)y turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

  What is the total amount of energy stoy.b(vm 3q; vnbgox0w 7red in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, caudr9/ar5* lynjr;1llu bqvle ;:/ qw .n be used without blowing a 15-A fuser uyda.1:/l;/r;w l*qqenbu59vljr l?    bulbs

  An extension cord made of two wires of cw5nxvn 7,irmq8 i5l n v35k./gksg1g diameter 0.129 cm (no. 16 copper wire) and of lk v5i n8 sm 1nkiwr3q5lgv5x.c,gn7/ gength 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a fni w4;4- px39d unepaxactory through wires with total resistance 9 ;-44iann uwxe3x pdp$3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line is se zw/p7(; hfn17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by/ f pwh7z(ns;e no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be useieh5sm,gd+ feud n *5:0x fda)d in a car to heat a cup of water for coffee or tea. If the heater canefgd*a05u)if 5h:+x d,nsde m heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak curri/gcvn.h wh-6 ent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 fnrr/oq 6f 9s8V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of th6z2bm 8tbmsbtfn-6t/e $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating current in a 1500-W device is 5.4 A. What is th8i5fk * 7 9pp /tfzrol8enp5zae rms voltage acrle5t788fpf*pao5 /z ir n9 zkposs it?    V (Round to the nearest integer)

  An 1800-W arc welder is con/o yc7tg vz/6bnected to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated dy3llm,5c0 9yiu ie62ynrqh+)dy 9r fby a 3.0-hp pump connecteyrimcy)h5,d0l6ir+ dqy2u 9f e 9y3 lnd to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a :bza6us uk )qvcl)7fttc4q41$240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

  A 0.65-mm-diameter copper wireet ru7/ g(qq;f nm,t(s carries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current whenoejcg4a1dze682mx up*xtj( 9 22.0 mV is applied to its ends. If the dripj e8 xa(x24egm9dc u 1oz*tj6ft speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in tt 0ikfsdlot5+r+u+ py p, *ho(he Earth’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in the Earth’s atm/hz(am . ka7clx+tgw5osphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of the elecq(5zqxw(x i8w tric field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric no*c 5 )jo5 4aj-ylsc tfg6;kjpulse. The action potential is detected at a point 3.40 cm down theon6 4sc ;gjoyc5a-*jfkj5 lt) axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one nqhl 7.b*7gv uaction potential along the axon of Example 18–15. [Hint: the energy to transmit lb*uq 7 ghn7.vone pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potd5at c5f-p(5v5+ taerlj- yli ential, $Na^+$ ions move into the cell at a rate of about $3 \times10^{-7 }\;mol/m^2\cdot s$. How much power must be produced by the “active $Na^+$ pumping” system to produce this flow against a $+30-Mv$ potential difference? Assume that the axon is 10 cm long and $20\mu m$ in diameter.    $ \times10^{-9 }\;W$

  How many coulombs are there de4i1( sffhx;in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motor? 2k o3y;ni l/jl$(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the3(frj,kywp :otg* c3q two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W 3yc(3, rfpowg*t:kqj , how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is 5.4 m long. If it is i +z+dxs1y9 sxurj14fmade of iron, whad 1 9++sjsrziu14fxyxt must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the r10jjs 03yfl5mxe p8yl4c1erz eciprocal of the resistance R; that isp yj41s3x0m8l0rel5 ejz1c yf , $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power. Suppose that instead of using high-vfo05;(1 yg yb+pxu(lu +i7h7bge abivoltage lines to supply the power,(+0 y 7fag1v byxh p (;ui5bbgeiu+7ol the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a49w.m+ :,p zh fh pmlz.ksgftb8n4 .gg 1.8-kW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the two lengths are wrappe x1hd ;d-0tphaxv, tj)gg+f5pd together side by side to make a thicker wix5ahdt jdt,h+x-vfgp)1g ;0pre. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for (qro:/-zrb yw117 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so it doe6+ nhbkeuh3gz++l w2f s not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1 hz3 6w h2++ugfenkbl+.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equati9sf thl9(pa;ron $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 950 r4i l d/mq ;37ybh;zb9:blvuwW of energy per second to the interior. Findlb ;y;7blb9/iw3dur:4 z qvmh
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conductors madep+72w z+i irgg of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of thgi+7izp+r gw2e power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater ibk-b s t,:e/kqs used to heat a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 24 yudhagr9 9cxh2mffd;*g) cpmja,* 1)0-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of stora nxlff n910i:dge batteries as its source of energy. Its mass is 1560 kg and it is powere:1nnx 9lifd f0d by 24 batteries, each 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

  A 100-W, 120-V lightbulb has a resistance ov.;o98 g iu vo37sniwof $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Illinois) is designed to carry an 11-mpzl /rv6 2u(feA beam of protons traveling at very nearly the r6u(f ev2 z/lpspeed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V a8hqlu n5gr 4)pkfp v/2c. The connecting cord is copper wire with a dl25v )/8uqrhfp n4pkgiameter of 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected nr2z st.a2 gic 3u1hy:to 120 V. The heating element is a coil of Nichrome wire. When un tr2 n:su1cay3ig2.hzcoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is o +nfia22xro-tff to about 13.8 V when the car is on and the charging sysi ar22 +o-fxtntem is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for householdv( r4o 5wvn046essiqj applications. Lightbulb B is rated at 12 V and 40 W for 4jni0r w4(5qvov e6ss automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of applianceuo m ,6w td72vib1os qvh*om5l 0c9ks9s at 120 V, which draw 2290 5lovchmwv1 k,7ot6i* ubqd s 9mso250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and an outside diameter of 5.00 /5 dwgyxno(ii 3 miuzlar-7up97d3 .c cm (Fig. 18–37). What is tlyz id(ud urc73i93a p5 -. mni/og7xwhe resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its lengthxs/o6w b5pn0 u doubles, by what factor does thex0nwb6 pu5s/ o power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashl0oy)g h 3mi8bvight bulb operates at 0.20 A and 3.2 V. If its yvho3b0 im)g8 resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$